PTEROPODA. 21 



three points. The mouth with two small tentacula is situated be- 

 tween the wing-s towards the closed side of the shell and above two 

 small eyes, and the genital aperture, whence issues a small penis in 

 the shape of a little proboscis. It is so diaphanous, that the heart, 

 brain, and viscera can be distinguished through the envelopes*. 



Pneumodermon, Cuv. 



The Pncumodernia begin to be a little further removed from the 

 Clios. Their body "is oval, without a mantle and without a shell ; the 

 branchife are attached to the surface, and composed of little laminae, 

 arranged in two or three lines so disposed as to form an H on the 

 part opposite to the head The fins are small ; the mouth which is 

 furnished with two small lips and two bundles of numerous tentacula, 

 each terminated by a sucker, has a little lobe or fleshy tantaculum 

 beneathf. 



Pneumodermon Peronii, Cuv. Ann. du Mus., IV, pi. 59 ; 

 and Peron, lb., XV, pi. 2. Not more than an inch long. The 

 species known was captured in the Ocean by Peron. 



LiMACiNA, Cuv. 



The Limacince, according to the description of Fabricius, should have 

 been closely related to the Pneumoderma ; but their body terminates 

 in a spirally convoluted tail, and is lodged in a very thin shell formed 

 by one whorl and a half, vuibilicated on one side, and flattened on the 

 other. The animal uses its shell as a boat, and its wings as oars, 

 whenever it wishes to navigate the surface of the deep. 



The species known Clio helicina, Phips and Gmel. ; Argonauta 

 arctica, Fab., Faun. Groenl., 387, is almost as common on the 

 Arctic seas as the Clio borealis, and is considered as forming 

 one of the chief sources of food for the Whale|. 



Hyalea, Lam., — Cavolina, Abildg. 



Have two large Avings ; no tentacula ; a mantle cleft on the sides, 

 lodging the branchice in the bottom of its fissures, and invested by a 

 shell also cleft laterally, the ventral face of which is arched, and the 

 dorsal flat and longer than the other ; the transverse line which 

 unites them behind, is furnished with three sharp dentations. When 

 alive, the animal thrusts several appendages, that are more or less 



* See Peron, Ann. Mus., X^', pi. iii, f. 10 — 11. N. B. in the fig. of Cymbulia, 

 piven by Blainville, Malac, XLVI, the position of the animal in the shell is directly 

 the reverse of the true one. Our description is founded upon the recent and re- 

 peated observations of M. Laurillard. 



t M. de Blainville once thought that the fins supported the branchial tissue, and 

 that what I have considered as branchiiE is another kind of fin. In this case the 

 analogy with the Clios would have been greater ; but since then, (Malacol., p. 483) 

 that gentleman has adopted my views. 



I I am not sure that the animal drawn by Scoresby, of which de Blainville 

 (Malac., pi. xlviii. bis, f. 5) makes his genus Spiratella, is, as he thinks, the same 

 as those of Phips and Fabricius. 



